It always amazes me how people agonise over buying machines, and need to justify. For what its worth here's my thoughts, hope it helps....
Remembers that whatever, and whenever you buy, it will be out of date within 3-6 months. I've been in the IT industry for 20 years and its been the same for the whole of that time...and it probably will be for the next 20.
So ask yourself these questions....
What do I need it to do?
When do I need to do it?
How much money do I have to spend?
How long will I keep it?
Then buy the machine that fits the bill.
If you need the machine now, buy it. If you don't need it, wait and buy the machine that fits the bill when you do need it.
If you just want the machine now then fine, I think we can all relate to that(!), so give into the temptation and have fun. If money isn't an issue then just buy the latest and greatest when it comes out in a few months. Remember Macs hold their value much better than PC's you've only got to look at Ebay and see the prices that 2 year old machines are still achieving, so it won't cost you a lot to upgrade.
To answer the original questions, will we see a MB upgrade in June. Possibly. Intel seem to be aggressively rolling out new chipsets and Apple seem to be following suit at the moment, that's why we saw the Penryn update, but will another chip update really make a difference to your use?
I needed to buy a new machine in the last month as a change of job saw me lose my HP laptop. It was just after the Penryn update arrived. So, I bought a refurb SR 2.2 Blackbook. Why? It fits the bill perfectly and I saved some 30% of the price of a Penryn. Do I notice the difference in power? Nope, goes very well for what I need it to, especially with the 4GB RAM I added for next to nothing. The 160GB drive is fine for me. Do I miss the extra battery life? Well I'm getting over 4 hours of use from each charge which is plenty thank you very much......
Will June see a lighter redesigned MB with LED screen, backlit keyboards and multi-touch? Personally I doubt it, as you have to consider the Apple laptop product range. There are three separate products here and each have their own markets and unique selling points. The MB already looks extremely good value compared with the Air and the MBP, and Apple will continue to differentiate their product lines in order to maintain healthy sales and profit margins. If Apple offered an Aluminium MB with LED, backlit keyboards, multitouch etc etc, then how many people would buy these instead of the not-as-well-specced-but-slightly-lighter-but-costs-twice-as-much-Air? Loads, thats how many, and Apple just aren't going to do that.....
....until, they further differentiate the Air and the MBP with the next set of innovations/upgrades. Then we will see all of these features arrive on the MB I am sure. Of course, all of this is personal opinion - if Apple did add all these things in June I'd happily eat my words and be first in the queue - at least I'd be able to sell my Blackbook for nearly what I paid for it!
So, best wishes, buy your Mac when you are ready and enjoy it. You will not look back!